Donald Trump's campaign is now auditing the spending of axed campaign manager Corey Lewandowski, according to the New York Post.

At issue is that Lewandowski ordered t-shirts and other campaign merchandise from a friend's Colorado-based company that sometimes cost the campaign more than four times the going rate – $8 per shirt, where other competitors could have done the work for $2.

Lewandowski used WizBang Solutions to make 'Make America Great Again' hats and other campaign swag, costing the Trump campaign $2.1 million, according to the Federal Election Commission report.

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Donald Trump's (left) former campaign manager Corey Lewandowski (right) used a Colorado based firm run by a business associate to print campaign swag - spending that is now being audited

Corey Lewandowski's use of the firm WizBang - which sold t-shirts for four times the price of other firms - was scrutinized by campaign chairman Paul Manafort, who ordered the audit

Mike Ciletti, the director of Wizbang, provided printing services to conservative group Americans for Prosperity when Lewandowski was working for the organization, the Post noted.

Ciletti, referred to as a 'longtime business associate' of Lewandowski's, briefly launched a super PAC for Trump – the Make America Great Again PAC – which was quickly shut down once the Washington Post reported the connections between the campaign and the PAC.

Trump had been self-financing his presidential run and having a super PAC would have watered down his popular message about money in politics and political corruption.

The Republican hopeful said publicly that he didn't sanction the super PAC, though Ciletti's association with Lewandowski made the campaign's relationship look rather cozy.

'It's an issue that I have relationships with Mr. Trump's staff,' Ciletti said to the Washington Post as he closed up shop in October 2015.

'I will eliminate the questions and shut down the super PAC,' Ciletti added.

According to the New York Post, Lewandowski first denied knowing Ciletti, but then acknowledged that he 'sort of' knew him.